The primary hyperoxalurias (PH), types 1–3, are disorders of glyoxylate metabolism that result in increased oxalate production and calcium oxalate stone formation. The breakdown of trans-4-hydroxy-L-proline (Hyp) from endogenous and dietary sources of collagen makes a significant contribution to the cellular glyoxylate pool. Proline dehydrogenase 2 (PRODH2), historically known as hydroxyproline oxidase, is the first step in the hydroxyproline catabolic pathway and represents a drug target to reduce the glyoxylate and oxalate burden of PH patients. This study is the first report of the expression, purification, and biochemical characterization of human PRODH2. Evaluation of a panel of N-terminal and C-terminal truncation variants indicated that residues 157–515 contain the catalytic core with one FAD molecule. The 12-fold higher kcat/Km value of 0.93 M−1·s−1 for Hyp over Pro demonstrates the preference for Hyp as substrate. Moreover, an anaerobic titration determined a Kd value of 125 μM for Hyp, a value ~1600-fold lower than the Km value. A survey of ubiquinone analogues revealed that menadione, duroquinone, and CoQ1 reacted more efficiently than oxygen as the terminal electron acceptor during catalysis. Taken together, these data and the slow reactivity with sodium sulfite support that PRODH2 functions as a dehydrogenase and most likely utilizes CoQ10 as the terminal electron acceptor in vivo. Thus, we propose that the name of PRODH2 be changed to hydroxyproline dehydrogenase (HYPDH). Three Hyp analogues were also identified to inhibit the activity of HYPDH, representing the first steps toward the development of a novel approach to treat all forms of PH.
- hydroxyproline metabolism
- hydroxyproline oxidase
Abbreviations: AGT, alanine:glyoxylate aminotransferase; AspAT, aspartate aminotransferase; o-AB, o-aminobenzaldehyde; CoQ1, Coenzyme Q1; GR, glyoxylate reductase; HOG, 4-hydroxy-2-oxoglutarate; HOGA, 4-hydroxy-2-oxoglutarate aldolase; HYPDH, hydroxyproline dehydrogenase; Hyp, trans-4-hydroxy-L-proline; LDH, lactate dehydrogenase; MB, menadione bisulfite; 4-OH-Glu, 4-hydroxy-glutamate; 3-OH-P5C, Δ1-pyrroline-3-OH-5-carboxylate; P5CDH, Δ1-pyrroline-5-carboxylate dehydrogenase; PH, primary hyperoxaluria; PRODH, proline dehydrogenase; PutA, proline utilization A; THFA, tetrahydrofuroic acid
- © The Authors Journal compilation © 2015 Biochemical Society